The present invention relates to an apparatus for conveying a lead frame mounting a number of semiconductor pellets thereon, in wire bonding.
In a wire bonding system, the lead frame on which the semiconductor pellets are mounted is intermittently conveyed by an apparatus for conveying lead frame at a predetermined feed pitch. The portion to be bonded of the lead frame and the portion to be bonded of the semiconductor pellet are guided to a predetermined position corresponding to a bonding tool of a bonding head placed on an X-Y table. Since the semiconductor pellet is very small and wire bonding requires a high precision of processing, the apparatus requires very high precision of conveying.
Generally, the lead frame conveying apparatus has a guide path for guiding the lead frame and a feed rod disposed along the guide path. The feed rod has an engaging portion which can be engaged with the lead frame. The feed rod is disposed to reciprocate along the guide path and is vertically movable between a position where the engaging portion of the feed rod engages with the lead frame and a position where the engaging portion becomes disengaged therefrom. The feed rod is intermittently driven by a driving means. The driving means has a motor as a driving source, a cam for vertically driving the feed rod which is attached to a rotating shaft of the motor, and a feed cam for reciprocally moving the feed rod which is attached to the shaft. Upon rotation of the motor, the feed rod is vertically moved by the cam, so that the engaging portion of the feed rod engages with the lead frame. At the same time, the feed rod is moved along the guide path by means of the feed cam. Thus, the lead frame is intermittently conveyed at a selected pitch.
However, in the apparatus with the above structure, the following drawbacks are presented. The cam for vertically moving the feed rod and the feed cam for reciprocally moving the feed rod are driven by a single driving source, that is, the motor. The members of the driving means are located in one place. Thus, the driving means is complex and hence the apparatus as a whole is complex. Further, the feed cam must be replaced by another in order to change the feed pitch of the feed rod, inevitably because the feed cam converts the rotation of the motor shaft to a linear motion of the feed rod. It takes a long time to replace the feed cam with another.